When a German submarine sank passenger liner RMS Lusitania on May, 1915, it redefined the laws of conflict. The loss of the boat and 1,198 lives shocked the world. But was the U-boat?s torpedo the only thing that sank the Lusitania? Or was a second reported explosion caused by an illegal cargo of weapons? Dark Secrets of the Lusitania plunges below the waves on a new expedition to venture into the wreck in a bid to get to the bottom of this century-old war crime.